reverting blinded envelope

[james-prysm]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

reverts the blinded envelop introduced in #16943 based on discussion and spec change on beacon api specs.

kurtosis test

participants:
  - el_type: ethrex
    el_image: ethpandaops/ethrex:glamsterdam-devnet-5
    el_extra_params:
      - --http.api=eth,net,web3,admin
    cl_type: prysm
    cl_image: gcr.io/offchainlabs/prysm/beacon-chain:latest
    vc_image: gcr.io/offchainlabs/prysm/validator:latest
    supernode: true
    cl_extra_params:
      - --verbosity=debug
    vc_extra_params:
      - --verbosity=debug
    count: 4

network_params:
  fulu_fork_epoch: 0
  gloas_fork_epoch: 1
  seconds_per_slot: 6
  genesis_delay: 30

additional_services:
  - dora
  - tx_fuzz

global_log_level: debug

Which issue(s) does this PR fix?

implements ethereum/beacon-APIs#624

Other notes for review

Acknowledgements

• I have read CONTRIBUTING.md.
• I have included a uniquely named changelog fragment file.
• I have added a description with sufficient context for reviewers to understand this PR.
• I have tested that my changes work as expected and I added a testing plan to the PR description (if applicable).